C++ Cross Platform Development

Build

• Combination of variants
• The variant combination should be build int own directory
• A variant may be:
  • Base OS
  • Processor architecture
  • GUI
  • Build tools and runtime libraries
  • Facilities
  • Versions (of OS, …)
  • Other …

Platform differences are variants

• Base OS
• Processor Architecture
• GUI
• Build tools and runtime libraries

Hiding behind API

• Define internal API with different implementations
• Place different implementations in different directories

Target hierarchies

• Classify - common/, arch/, os/, gui/ toolset/, etc.
• Arrange source to reflect classification os/win/ce/3.0/src
• Specify target attributes to build system as hierarchy OS=win/ce/3.0

Depth override

• Search for target-specific version of the source file
• Search in defined order, common last
• If file is not found, drop attribute element from the right of hierarchy and try again
• More specific code is foudn further right of the tree

Considerations

• Plan to let it evolve
• Be prepared to refactor code
• Write code at the leaves and push up - easy to identify portability work
• Regular automated build/test for all platforms - find problems quickly

Code

• Specify category order
• Subcategories can have elements removed until empty
• Don’t allow duplicate locations

Build Systems

• GNU Make
• NMake
• XCode
• MSBuild

CMake

• Most widely used - de facto standard
• Should learn the language and best practices
• Problem - reproduce configuration and build
• Build each from source - ExternalProject_Add
• find_package - Config files: XXXConfig.cmake, CMAKE_PREFIX_PATH
• Find modules : (not cmake dependent) - FindXXX.cmake, CMAKE_MODULE_PATH
• Packaging: CPack
• Testing: Ctest
• Toolchains: CMAKE_TOOLCHAIN_FILE , Conan profiles
• FetchContent - downloads at configure time, doesn’t scale

Common configuration

• File: CMakePresets.json
• Common configure options and share with others. Integrated in Visual Studio Code
• Example: https://github.com/WillBuik/pong
• ACCU 2021 example: https://github.com/esweet431/box2d-lite
• Documentation cmake-presets
• CMakePresets.json and CMakeUserPresets.json Microsoft vendor maps

Dependency management

• No automation and reproducible dependency management
• System package managers: apt
• Build system specific package managers: NuGet
• Language specific package managers: vcpkg
• Conan -> recommended for C++ cross platform development

Debugging

• Multiple platform specific debugging tools
• GUI vs Command driven interface
• Core dumb debugging
• Debugging crashes on CI

Cross platform IDE

• CLion
• VS Code
• Qt Creator

References

• Cross-Platform Pitfalls and How to Avoid Them - Erika Sweet
• Building and Organising a Multi-Platform Development Code Base - Jim Hague
• Building Portable C++ Packages: The Curse of Abundance - Piotr Gaczkowski
• Building Portable C++ Packages: The Bliss of Unification - Adrian Ostrowski
• github.com/Perl/metaconfig
• doomhammer.info
• https://github.com/aostrowski